1. Field of the Invention
The present invention relates to a light source apparatus and an image display apparatus having the same, more particularly to a light source apparatus that is suitably used in an apparatus such as a projector or a head mount display that enlarges for viewing, through an optical system, an image formed by light beams optically modulated by a liquid crystal display element.
2. Description of the Related Art
There has been known a light source apparatus that creates, using light beams from a primary light source, a secondary light source surface on a diffusion surface and illuminates a liquid crystal display element with light beams from the secondary light source surface directly or via an illumination optical system.
A light source that uses as a light source a fluorescent lamp or a plurality of light emitting diodes (LED) arranged on a substrate has been known (see Japanese Patent Application Laid-Open No. 2003-140110).
There have been known a liquid crystal projector and a head mounted display (HMD) that illuminate an image display element such as a liquid crystal display element with light beams from a light source of the aforementioned type and enlarges an image displayed on the image display element through an optical system to present an enlarged image to an observer.
There has also been known a projector that uses a light source apparatus of the aforementioned type and a decentered free-form surface optical system to project an image from an oblique direction (see U.S. Pat. No. 7,021,770).
In a known observation optical system, an optical system having a decentered free-form curved surface is used to make the overall size of the apparatus small while enhancing the realism of the image by making the angle of view wide (see Japanese Patent Application Laid-Open No. H07-333551 and U.S. Pat. No. 7,019,909).
There has also been known an image observation apparatus that uses a reflection type liquid crystal display element having a high aperture ratio as a small, high-definition display panel and forms an image through optically modulation by the liquid crystal display element to present it for observation (see U.S. Pat. No. 6,480,337).
In the image observation apparatus such as the HMD, it is preferred that the light source apparatus be designed to have directivity in illuminating a liquid crystal display element with light beams from a secondary light source surface so that the direction in which the brightness is maximum is not the direction normal to the secondary light source surface but the direction of the center field angle chief ray. Here, the center field angle chief ray refers to the chief ray emerging from the center of the image displayed on the liquid crystal display element and incident on the center of the exit pupil of the optical system.
A light source apparatus having directivity toward a direction other than the direction normal to the light source is also known (see Japanese Patent Application Laid-Open No. 2000-057832). Japanese Patent Application Laid-Open No. 2000-057832 teaches to arrange a plurality of light sources each of which is covered with a reflector, and cover spaces between the reflectors with reflection plates so that light emerging from the reflectors and light reflected by a transmission type liquid crystal display element and then reflected by the reflection plates of the light source apparatus serve as illumination light.
To present a good image in a liquid crystal projector that uses a liquid crystal display element, it is important to illuminate the liquid crystal display element uniformly and efficiently with light beams emitted from a light source apparatus. In the liquid crystal projector using a reflection type liquid crystal display element, the structure of the light source apparatus for illuminating the liquid crystal display element is generally complex, illuminance on the liquid crystal display element is likely to be uneven, and it is very difficult to illuminate the liquid crystal element efficiently at a high luminance. In illuminating, in particular, a reflection type liquid crystal display element, it is important to appropriately arrange the directivity of light beams emitted from the light source apparatus.
There have been no conventional light source apparatuses in which directivity of light beams emitted from a light source apparatus is appropriately arranged by a simple structure in illuminating a liquid crystal display element.